The present invention relates to a cryogenic transport hose. More particularly, the invention relates to a lightweight, flexible hose capable of transporting cryogenic fluids, especially cryogenic liquids, especially for use in connection with cryosurgical procedures.
In the prior art, the hoses have been developed for the purpose of supporting the movement of cryogenic fluids. However, effectiveness of such hoses has been limited since it has been difficult to design such a hose with sufficient insulative properties to limit heat gain of the liquid cryogen over any significant distance. In fact, the development of the field of cryosurgery has been limited in part by the inability to transport a boiling liquid any significant distance without gasification.
In designing a cryogenic transport hose, the following characteristics must be incorporated:
(1) Low thermal conductance: the hose must be provided with sufficient insulative properties to limit the degree of temperature gain of the cryogenic fluid per unit length; PA1 (2) High degree of flexibility: the materials from which the hose is constructed must maintain flexibility even at temperatures below -100.degree. C.; PA1 (3) Reliability: the hose must be constructed in such a manner that it will not leak and will not fail even though subjected to numerous cycles of cooling and subsequent warming; this is especially important in the intended application in connection with cryosurgical probes; PA1 (4) Soft, pliable outer covering: the hose must have an outer covering which is not abrasive when handled by the user but which provides adequate protection against rough handling, is easily applied and provides an attractive appearance; PA1 (5) Tolerance to twisting and lateral deformation: as pointed out in (2) above, the materials from which the hose is constructed must be sufficiently flexible to prevent failure regardless of the contortions to which the hose is subjected. The ability to be twisted, flexed, etc. also allows the hose to be folded, or looped into a small compact configuration for storage and shipping.
Additionally, given the state of the art concerning cryosurgical instruments, the hose must be provided with a fluid connector allowing secure, reproducible and quick connection to a source of cryogenic fluid. Furthermore, the hose must be provided with a coupling at its distal end allowing coupling of the hose to various types of cryogenic surgical probes. Additionally, it would be advantageous to provide such a hose with means facilitating monitoring of the temperature of the cryogenic fluid at the hose/probe coupling and/or the temperature of or at the probe tip.
It is with these aspects in mind that the present invention was developed.
The following prior art is known to Applicants:
U.S. Pat. No. 3,269,422 to Matthews et al. discloses a composite tubing product and apparatus and method. In the embodiments of Matthews et al., metallic tubes are surrounded by a layer of filler material which in some embodiments, is surrounded by a wrapping "such as for instance a laminated Dacron-asbestos tape known as Mylar and having good heat insulating characteristics." The present invention differs from the teachings of Matthews et al. as contemplating the use of flexible, plastic conduits directly surrounded by an insulative wrapping.
U.S. Pat. No. 4,194,536 to Stine et al. discloses a composite tubing product including two inner tubes in heat transfer relationship surrounded by a flexible thermal barrier of multiple layers of low bulk, low density fibrous glass. A filler of fibrous or foam material is present between the tubes and the barrier layer and a binder member, which may comprise metallic film, may be wrapped around the tubes to secure a heating line spirally wrapped around the tubes. Of course, in the present invention, the intent is to maintain cryogenic fluid within two conduits as cool as possible. Thus, the teachings of Stine et al. appear to be at cross-purposes with the teachings of the present invention.
U.S. Pat. No. 4,380,253 to Mead et al. discloses a heat-insulated hose for liquified gases which includes an inner hose resistant to cyrogenic temperatures and a plurality of successive layers of heat insulating material. In the preferred embodiment, Mead et al. contemplates the insulating layers as comprising a plurality of layers of polystyrene foam with intervening layers of Mylar film. The Mylar film of Mead et al. is not disclosed as metallized. The present invention differs from the teachings of Mead et al. as contemplating surrounding two cryogenic fluid conveying conduits directly with a plurality of layers of metallized reflective foil and surrounding the layers of foil with foam.
U.S. Pat. No. 4,924,679 to Brigham et al. discloses apparatus and method for evacuating an insulated cryogenic hose. As disclosed by Brigham et al., vacuum insulation is provided as an insulative layer. Also disclosed is the use of a wrinkled reflectorized foil sheet surrounding the cryogenic conduit. As a modification, Brigham et al. illustrate, but do not discuss, use of a urethane foam insulation layer. The present invention differs from the teachings of Brigham et al. as contemplating a cryogenic transport hose wherein supply and return conduits are directly surrounded by a plurality of layers of reflective metallized foil material surrounded by a foam insulative layer. The present invention is advantageous as compared to the teachings of Brigham et al. since vacuum insulation layers have proven unreliable in cryogenic transport hoses since the twisting and lateral deformation of such hoses, in use, along with multiple cooling/warming cycles, often cause the vacuum layer to fail.
U.S. Pat. No. 5,072,591 to Grange et al. discloses a flexible transfer line exhaust gas shield. In Grange et al., a flexible transfer line is supported within a plastic tube around which is wrapped a shield of flexible metal braid or tape surrounded by a super-insulation layer. The present invention differs from the teachings of Grange et al. as contemplating a hose containing supply and return conduits made of flexible plastic, surrounded by multiple layers of metallized reflective foil and surrounded by a foam insulation layer.